Evaluation of the effectiveness of a desulphurized tailings cover at Detour Lake Mine
Dobchuk, Bonnie Sjoberg
Cover technology has developed over the last decade as a remediation option to reduce acid rock drainage from mine tailings. Desulphurized tailings have been investigated as a cover material due to their potential to consume oxygen, hydraulic properties and relative abundance at mine sites. A desulphurized tailings cover was installed at the Detour Lake Mine to cover a portion of the tailings impoundment. The desulphurized tailings cover was intended to reduce oxygen penetration into the sulphidic tailings by maintaining saturation to reduce oxygen diffusion and by consuming oxygen by oxidation of the remaining sulphide minerals. A research study was initiated to evaluate the effectiveness of this cover at reducing oxygen penetration into the sulphidic tailings. The scope of the research involved a field investigation, laboratory analysis and numerical modeling. The field investigation involved instrumenting the tailings impoundment to measure weather data, water levels and water content. Tailings samples were evaluated in the laboratory investigation for geotechnical and geochemical characteristics. The purpose of the field and laboratory investigation was to satisfy two objectives: to yield qualitative conclusions regarding the effectiveness of the desulphurized tailings cover and to establish representative profiles for the numerical modeling. The purpose of the numerical modeling was to evaluate the oxygen concentration through various tailings profiles to determine the relative effect of weather, vegetation and water table depth. The program SoilCover and a finite difference program were used for this evaluation. The general conclusion from this research was that the desulphurized tailings cover is likely not reducing oxygen penetration into the sulphidic tailings to very low levels over the entire tailings surface. The factors acting to reduce the oxygen penetration are the ability of the sulphidic tailings to remain saturated well above the water table, the consumption of a portion of the oxygen by kinetic oxidation and the potential, based on field observations, for fine tailings layers within the tailings profiles to act as oxygen barriers.